1. Field of the Invention
The present invention relates to a compound semiconductor device.
2. Related Background Art
Patent Literature 1 (Japanese Patent Application Laid-open No. 2004-172568) discloses a nitride semiconductor device having a counter-electrode structure. An n-polar surface of this nitride semiconductor at least includes a tilting surface which is different from a surface (000-1), and is provided with an electrode. The n-polar surface of this nitride semiconductor has unevenness. Furthermore, the tilting surface differing from the surface (000-1) is located on a side of bump of unevenness, and has an off angle from the surface (000-1) in a range of not less than 0.2° and not more than 90°. Patent Literature 2 (Japanese Patent Application Laid-open No. 2005-129696) discloses a semiconductor device (HFET). The HFET has a first nitride semiconductor layer formed on a buffer layer on a SiC substrate; a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer producing a two-dimensional electron gas layer in an upper part of the first nitride semiconductor layer; and two ohmic electrodes selectively formed on the second nitride semiconductor layer. The second nitride semiconductor layer includes a contact portion having a tilting portion of which the cross section shape is concave shape. The bottom surfaces or the side surfaces of the tilting portion tilt from the substrate surface. The two ohmic electrodes are formed on the contact portion.
Patent Literature 3 (Japanese Patent Application Laid-open No. 2007-116076) discloses a semiconductor device including an n-electrode having low contact resistance on a nitrogen polar surface of gallium nitride (GaN)-based semiconductor. The semiconductor device has a group-V atom vacancy region having a ratio (the number of group-III atoms)/(the number of group-V atoms) of more than 1 at a portion in contact with the n-electrode. Patent Literature 4 (International Publication No. WO2006/098215) discloses a nitride semiconductor device. The nitride semiconductor device has an n-type GaN substrate; a layered semiconductor structure which includes a p-type region and an n-type region and is formed on a principal surface of the n-type GaN substrate; a p-side electrode in contact with a part of the p-type region included in the layered semiconductor structure; and an n-side electrode provided on the backside of the n-type GaN substrate. In the nitride semiconductor device, the backside of the n-type GaN substrate includes a nitrogen surface, and a carbon concentration of the interface between the backside and the n-side electrode is adjusted within a range of not more than 5 atomic percent.